PING problem

I have a very small network with 4 systems on it - 2
Win98SE and 2 XP Pro. All are attached to a D-Link 4-
port DSL/Cable router. Everything works fine in terms of
accessing the Internet. However, the 2 Win98 PCs won't
respond to a PING request (specifically, they never
respond to the initial ARP broadcast sent by the
PINGer). I can PING both XP Pro PCs from any PC, but I
can't successfully PING either Win98 PC from either XP
Pro PC or the other Win98 PC. All systems can PING the D-
Link router.

All systems have an appropriate (and unique) IP address
and the correct subnet mask (Class C), which are provided
by the D-Link router. I switched out the D-Link for a
known good Linksys router - same problem. I updated the
NIC drivers on one of the systems - same problem. I have
some other things I want to do, but don't want to proceed
until I know everything is working properly. I'm
stumped. Any suggestions would be greatly appreciated.

Update - Attached is a trace file showing the problem.
It seems that the Win98 PCs (both of them) respond to the
PINGer's ARP with the correct MAC address, but when the
PINGer then sends the ICMP Request to the PINGee, the
PINGee never responds.

No. Time Source
Destination Protocol Info
1 0.000000 192.168.1.152
Broadcast ARP Who has 192.168.1.101?
Tell 192.168.1.152
2 0.000151 192.168.1.101
192.168.1.152 ARP 192.168.1.101 is at
00:50:ba:e8:63:e0
3 0.000158 192.168.1.152
192.168.1.101 ICMP Echo (ping) request
6 5.313473 192.168.1.152
192.168.1.101 ICMP Echo (ping) request
7 10.814031 192.168.1.152
192.168.1.101 ICMP Echo (ping) request
8 16.314578 192.168.1.152
192.168.1.101 ICMP Echo (ping) request